Multi-wavelength transparent microfluidics for UV-visible spectroscopy and X-ray scattering studies of photoactive systems

TL;DR

This paper introduces a versatile, easy-to-fabricate microfluidic device that is transparent to UV, visible, and X-ray light, enabling advanced studies of photoactive liquids and proteins at synchrotrons.

Contribution

The authors present a novel multi-wavelength transparent microfluidic device fabricated via lamination and UV lithography, suitable for UV-visible spectroscopy and X-ray scattering studies.

Findings

Validated UV-visible transparency through reversible photoisomerization of azobenzene derivatives.

Confirmed X-ray transparency with SAXS measurements on hemoglobin samples.

Demonstrated potential for temperature-jump and pump-probe experiments in structural studies.

Abstract

Microfluidic devices are increasingly used in synchrotron-based experiments to deliver and probe liquid samples, offering advantages such as minimal sample consumption and reduced radiation damage. Despite their growing use, few devices have been specifically designed for monitoring liquids under photoexcitation, a promising approach for fast structural transitions. Here, a microfluidic device that is transparent to X-rays in one direction, and simulaneously transmits UV and visible light in the perpendicular direction is presented. The device is fabricated using lamination and UV lithography on a dry-film resist, eliminating the need for cleanroom facilities and simplifying production. Its multi-wavelength transparency was validated through UV-visible spectroscopy, where photoexcitation at different wavelengths induced reversible trans-to-cis isomerization of azobenzene and fluoro-azobenzene. X-ray transparency was validated through Small Angle X-ray Scattering (SAXS) measurements on hemoglobin and CO-ligated hemoglobin sensitive to quaternary structural changes. These resusts confirm the suitability of the device for resolving protein structures and photoinduced conformational dynamics. The design further supports, as some proof of concept results show, temperature-jump and time resolved pump-probe experiments, providing a versatile platform for studying structural evolution in liquid samples using synchrotron SAXS.